A vane pump construction of the type referred to above is disclosed in U.S. Pat. No. 2,570,411 issued to H. F. Vickers.
The Vickers' pump disclosed in the above mentioned patent includes a pumping cartridge comprising a three-part rotor and a pair of duplicate liner rings having oval cylindrical inner surfaces surrounding the three-part rotor. The liner rings are mounted for conjoint rotation between a pair of flange bushings.
The three-part rotor includes two identical main rotor elements journaled in the bushings and a separator disc mounted between the rotor elements and having a peripheral portion extending into a recess provided in the rings. The rotor elements are provided with a plurality of recesses each of which carries a radially slidable vane forming two rows of vanes, one row on each side of the separator disc with the radially outermost tips of the vanes, maintained by fluid pressure, in slidable contact with the inner contour of the rings. The separator disc functions to maintain the vanes in axial alignment with their respective rings.
Means are provided for manual rotary adjustment of the rings from a first position in which the inner contours of the rings are in register with each other for pumping full capacity through the cartridge, to a second position in which the inner contours are again in register with each other but transposed from the first position for pumping full capacity through the cartridge in an opposite direction.
However, it is believed that the pumping cartridge with the three-part rotor design described above has certain disadvantages. Among the disadvantages are the multiplicity of parts leading to increased leakage paths resulting in low volumetric efficiency; low overall efficiency; and high manufacturing costs.
The volumetric efficiency of a pump is defined as the ratio of actual output of the pump in gallons per minute to the theoretical or design output of the pump. The actual pump output is reduced because of internal fluid leakage. As pressure increases, the leakage of fluid from the outlet back to the inlet and/or tank increases and volumetric efficiency decreases.
The overall efficiency of a pump is defined as a ratio of the output hydraulic horsepower of the pump to the input horsepower of the pump drive. Hydraulic horsepower is defined as the product of fluid flow in gallons per minute; the fluid pressure in pounds per square inch; and a constant coversion factor of seven ten thousandths (0.0007). The overall efficiency reflects the internal power losses in a pump due to leakage and friction between the moving parts. An increase in leakage or friction will reduce the overall efficiency of the pump.
The multiplicity of parts in the above noted pumping cartridge results in an axial tolerance build-up inherent in the three-part construction. If the parts of the cartridge are toleranced to insure rotatability of the rings, the efficiency of the pump is reduced to unacceptable levels as compared to a comparable conventional fixed displacement vane pump. This reduction in efficiency is due to excess fluid leakage between the parts. Additionally, the pump efficiency is believed to be affected by turbulence of the fluid flow between adjacent pumping chambers which is induced by the presence of the separator disc therebetween.
It is an object of the present invention to provide a variable displacement vane pump wherein the full displacement volumetric and overall efficiencies approach that of a comparable conventional fixed displacement vane pump.
It is another object of the present invention to provide a variable displacement vane pump wherein the liner rings are readily rotatable relative to each other.
Still another object of the present invention is to provide a variable displacement vane pump operable in a pressure compensated mode.
To this end, a variable displacement vane pump is provided which includes a casing having an inlet and an outlet. A cavity is formed in the casing between the inlet and the outlet. A pair of rings having oval-shaped inner contours are rotatably mounted in the cavity in side-by-side relationship. The rings are adapted for relative rotation to each other between a first position wherein the inner contours are in register and a moved position wherein the inner contours are out-of-register. Means are provided, operatively connected to the rings, for effecting their relative rotation. A rotor having a plurality of circumferentially spaced recesses is mounted in the cavity for rotation within the rings. A pair of vanes are movably mounted in abutting relationship in each of the recesses and are adapted for slidable contact with the inner contours of the rings.
These and other objects and features of my invention will become apparent with reference to the following description and drawings taken together with the appended claims.